Removable embolus blood clot filter

ABSTRACT

A removable blood clot filter includes a number of locator members and anchor members disposed radially and extending angularly downward from a hub. The locator members include a number of linear portions having distinct axes configured to place a tip portion approximately parallel to the walls of a blood vessel when implanted and to apply sufficient force to the vessel walls to position the filter near the vessel centerline. The anchor members each include a hook configured to penetrate the vessel wall to prevent longitudinal movement due to blood flow. The hooks may have a cross section sized to allow for a larger radius of curvature under strain so that the filter can be removed without damaging the vessel wall.

PRIORITY DATA AND INCORPORATION BY REFERENCE

This application is a continuation of U.S. patent application Ser. No.11/429,975, filed May 9, 2006, now U.S. Pat. No. 7,967,838, which claimsthe benefit of priority to U.S. Provisional Patent Application No.60/680,601, filed May 12, 2005, which is incorporated by reference inits entirety into this application.

FIELD OF THE INVENTION

This invention relates to a filter device that can be placed in a bloodvessel to reduce the risk of embolisms and, if needed, removed from theblood vessel without causing traumatic damage to the blood vessel.

BACKGROUND OF THE INVENTION

In recent years, a number of medical devices have been designed whichare adapted for compression into a small size to facilitate introductioninto a vascular passageway and which are subsequently expandable intocontact with the walls of the passageway. These devices, among others,include blood clot filters which expand and are held in position byengagement with the inner wall of a vein, such as the vena cava. Thesevena cava filters are designed to remain in place permanently. Suchfilters include structure to anchor the filter in place within the venacava, such as elongate diverging anchor members with hooked ends thatpenetrate the vessel wall and positively prevent migration in eitherdirection longitudinally of the vessel. The hooks on filters of thistype are rigid and will not bend, and within two to six weeks after afilter of this type has been implanted, the endothelium layer grows overthe diverging anchor members and positively locks the hooks in place.Now any attempt to remove the filter results in a risk of injury to orrupture of the vena cava.

A number of conditions and medical procedures subject the patient to ashort term risk of pulmonary embolism which can be alleviated by afilter implant. In such cases, patients are often averse to receiving apermanent implant, for the risk of pulmonary embolism may disappearafter a period of several weeks or months. However, most existingfilters are not easily or safely removable after they have remained inplace for more than several weeks, and consequently longer-termtemporary filters that do not result in the likelihood of injury to thevessel wall upon removal are not available.

In an attempt to provide a removable filter, two filter baskets havebeen formed along a central shaft that are conical in configuration,with each basket being formed by spaced struts radiating outwardly froma central hub for the basket. The central hubs are held apart by acompression unit, and the locator members of the two baskets overlap sothat the baskets face one another. Filters of this type require the useof two removal devices inserted at each end of the filter to draw thebaskets apart and fracture the compression unit. The end sections of thelocator members are formed to lie in substantially parallel relationshipto the vessel wall and the tips are inclined inwardly to preclude vesselwall penetration. If a device of this type is withdrawn before theendothelium layer grows over the locator members, vessel wall damage isminimized. However, after growth of the endothelium layer the combinedinward and longitudinal movement of the filter sections as they aredrawn apart can tear this layer.

SUMMARY OF THE INVENTION

The various embodiments provide for a removable blood filter that allowsfor filtering of an embolus in a blood vessel by utilizing a pluralityof locators and a plurality of anchors. In one aspect, a filter to beplaced in a flow of blood through a vessel includes a hub, at least oneanchor, and at least one locator. The hub can be disposed along alongitudinal axis. The at least one anchor projects from the hub andincludes a hook that penetrates a wall of the blood vessel when thefilter is placed in the blood vessel. The hook can be spaced along thelongitudinal axis from the hub and spaced a first radial distance fromlongitudinal axis. The at least one locator has a tip or portion of thelocator that engages the wall of the vessel. The tip can be spaced alongthe longitudinal axis from the hub and spaced a second radial distancefrom the longitudinal axis. The second radial distance can be less thanthe first radial distance. The at least one locator has at least fourportions and each of the portions can be disposed on respective distinctaxes.

In yet another aspect, the various embodiments also provide for a filterto be placed in a flow of blood through a vessel. The filter includes ahub, at least one anchor, and at least one locator. The hub can bedisposed along a longitudinal axis. The at least one anchor projectsfrom the hub and includes a hook that penetrates a wall of the bloodvessel when the filter is placed in the blood vessel. The hook can bespaced along the longitudinal axis from the hub and spaced a firstradial distance from the longitudinal axis. The at least one locatorprojects from the hub and has a tip or portion of the locator thatengages the wall of the vessel. The tip can be spaced along thelongitudinal axis from the hub and spaced a second radial distance fromthe longitudinal axis where the second radial distance can be less thanthe first radial distance. The locator can be disposed proximate the huband has at least four portions, and each of the at least four portionscan be disposed on respective distinct axes. The at least four portionscan include a curved portion being disposed on a radius of curvaturethat extends along the longitudinal axis.

In yet a further aspect of the various embodiments, a filter is providedto be placed in a flow of blood through a vessel. The filter includes ahub, at least one anchor and at least one locator. The hub can bedisposed along a longitudinal axis. The at least one anchor projectsfrom the hub and includes a hook that penetrates a wall of the bloodvessel when the filter is placed in the blood vessel, spaced along thelongitudinal axis from the hub, and spaced a first radial distance fromlongitudinal axis. The at least one locator projects from the hub andhas a tip or portion of the locator that engages the wall of the vessel.The tip can be spaced along the longitudinal axis from the hub, andspaced a second radial distance from the longitudinal axis, where thesecond radial distance can be less than the first radial distance. Thelocator has a first portion distal to the hub and a second portionproximal to the hub. Each of the first and second portions can begenerally linear and disposed on distinct axes oblique with respect tothe longitudinal axis, where the length of the first portion can begreater than a length of the second portion.

In yet an additional aspect of the various embodiments, a filter isprovided to be placed in a flow of blood through a vessel. The filterincludes a hub, at least one anchor and at least one locator. The hubcan be disposed along a longitudinal axis. The at least one anchorprojects from the hub and includes a hook that penetrates a wall of theblood vessel, spaced along the longitudinal axis from the hub, andspaced a first radial distance from the longitudinal axis. The at leastone locator projects from the hub and has a tip or portion of thelocator that engages the wall of the vessel. The tip can be spaced alongthe longitudinal axis from the hub, and spaced a second radial distancefrom the longitudinal axis, where the second radial distance can be lessthan the first radial distance. The locator has first and secondportions oblique to the longitudinal axis. The first portion can bedistal to the hub, and a second portion can be proximal to the hub,where a length of the first portion being greater than a length of thesecond portion.

In yet another aspect of the various embodiments, a filter is providedto be placed in a blood vessel that includes a blood vessel wall. Thefilter includes a hub, and a first and a second set of members. The hubcan be disposed along a longitudinal axis. Each of the first set ofmembers extends from the hub. Each of the first set of members includesa hook spaced along the longitudinal axis from the hub, each hook beingspaced radially from the longitudinal axis a first distance. Each of thesecond set of members extends from the hub and includes a tip beingspaced along the longitudinal axis from the hub. Each tip can be spacedradially from the longitudinal axis a second distance less than thefirst distance.

In yet a further aspect of the various embodiments, a filter to beplaced in a blood vessel is provided. The filter includes a hub, aplurality of anchors and a plurality of locators. The hub can bedisposed along a longitudinal axis. The plurality of anchors branchesfrom the hub. Each anchor includes a hook that: (i) penetrates a wall ofthe blood vessel, (ii) can be spaced along the longitudinal axis fromthe hub, and (iii) can be radially spaced from the longitudinal axis afirst distance. The plurality of locators branches from the hub. Eachlocator includes a base portion proximate the hub, a first portion thatextends from the base portion and along a first axis, a second portionthat extends from the first portion and along a second axis, which canbe distinct from the first axis, and a tip portion that extends from thesecond portion and along a tip axis, which can be distinct from thefirst and second axes. The tip portion (i) engages the wall of the bloodvessel, (ii) can be spaced along the longitudinal axis from the hub, and(iii) can be radially spaced from the longitudinal axis a seconddistance, which can be less than the first radial distance.

In yet a further aspect of the various embodiments, a filter to beplaced in a blood vessel is provided. The filter includes a hub, aplurality of anchors and a plurality of locators. The hub can bedisposed along a longitudinal axis. The plurality of anchors branchesfrom the hub. Each anchor includes a hook that: (i) penetrates a wall ofthe blood vessel, (ii) can be spaced along the longitudinal axis fromthe hub, and (iii) can be radially spaced from the longitudinal axis afirst distance. The plurality of locators branches from the hub. Eachlocator includes a base portion proximate the hub, a tip portion that(i) can engage the wall of the blood vessel, (ii) can be spaced alongthe longitudinal axis from the hub, and (iii) can be radially spacedfrom the longitudinal axis a second distance, which can be less than thefirst radial distance, and an intermediate portion coupling the base andtip portion. The intermediate portion can include a first linear segmentextending from the base portion a first length along a first axis, whichcan be oblique with respect to the longitudinal axis and a second linearsegment extending between the tip portion and first portions a secondlength, which can be greater than the first length, and along a secondaxis, which can be oblique respect to the longitudinal axis and can bedistinct from the first axis.

In yet another aspect of the various embodiments, a filter is provided.The filter is to be placed in a flow of blood contained by a wall of ablood vessel. The filter includes a hub that extends along alongitudinal axis and at least one first member having first and secondgenerally linear segments. The filter also includes at least one secondmember having third and fourth generally linear segments. The firstsegment defines a portion of a first cone when the first segment isrotated about the longitudinal axis. The second segment defines acylinder when the second segment is rotated about the longitudinal axis.The third and fourth segments define respective portions of a third andfourth cones when each of the segments is rotated about the longitudinalaxis. At least one of the third and fourth segments has a hook portionthat penetrates the wall of a blood vessel.

In yet a further aspect of the various embodiments, a blood filter isprovided to be placed in a flow of blood contained by a wall of a bloodvessel. The filter includes a hub, at least one anchor and a pluralityof locators. The hub can be disposed along a longitudinal axis extendinggenerally parallel to the flow of blood. The at least one anchorincludes a hook that penetrates the wall of the vessel. The at least oneanchor defines a generator of a first conical shape about a longitudinalaxis. The first conical shape includes: (i) an apex disposed proximatethe hub, each anchor (ii) can be spaced along the longitudinal axis fromthe hub, and (iii) can be radially spaced from the longitudinal axis ata first distance. The plurality of locators branches from the hub anddefines a first frustum having a geometric centroid along thelongitudinal axis.

In yet another aspect, a filter is provided. The filter can be placed ina flow of blood contained by a wall of a blood vessel. The filterincludes a hub, a plurality of anchors, and a plurality of locators. Thehub can be disposed along a longitudinal axis. The plurality of anchorsbranches from the hub. Each anchor can include a hook that (i)penetrates a wall of the blood vessel, (ii) can be spaced along thelongitudinal axis from the hub, and (iii) can be radially spaced fromthe longitudinal axis a first distance. The plurality of locatorsbranches from the hub. Each locator includes a base portion extendingarcuately from the hub. The base portion has a radius of curvature abouta transverse axis located at a second distance generally radially fromthe longitudinal axis. Each of the locators has a tip contiguous to thewall of the vessel. A portion of the tip closest to the hub can bespaced at a third distance along the longitudinal axis from the hub andspaced a fourth radial distance from the longitudinal axis, the fourthradial distance being less than the third distance.

The various embodiments described above may further include aradio-opaque material on or as part of the filter hub. Also, the variousembodiments described above may further include a bio-active agentincorporated with or as part of the filter.

The various embodiments further provide a method of centering a bloodfiltering device within a blood vessel having a plurality of locatorsextending from a hub to define a first volume and a plurality of anchorsextending from the hub to define a second volume. The method can beachieved by enclosing more than 15 percent of the second volume in thefirst volume, and engaging a hook provided on each locator onto a wallof the blood vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate presently preferred embodimentsof the invention, and, together with the general description given aboveand the detailed description given below, serve to explain features ofthe invention.

FIG. 1 is a top down perspective view of a preferred embodiment of theblood filter.

FIG. 2 is a bottom up perspective view of the embodiment of FIG. 1.

FIG. 3 is a plan view of the filter of FIG. 1 on longitudinal axis A.

FIG. 4A is a side view of the filter viewed along view 4A-4A in FIG. 3.

FIG. 4B is a side view of one arm or locator member of the filter ofFIG. 1.

FIG. 5A is a side view of the filter viewed along view 5A-5A in FIG. 3.

FIG. 5B is a side view of one locator member of the filter of FIG. 1.

FIG. 5C is a side view of an alternative locator arrangement having aretention member disposed on the locator.

FIG. 5D is a side view of another locator arrangement having a supportmember to reduce or prevent penetration of a blood vessel wall by thelocator.

FIG. 6 is a close up side view of a hook of the anchor member for thefilter of FIG. 1.

FIG. 7 is a shaded perspective view of a volume generated by the locatormember outside of a hub as it rotates or sweeps around longitudinal axisA.

FIG. 8 is a shaded perspective view of a volume generated by the anchormember outside the hub as the anchor member is rotated or sweeps aroundthe longitudinal axis A.

FIG. 9 illustrate the volume of the anchor member visible outside thevolume of the locator member.

FIGS. 10-14 illustrate yet another preferred embodiment having aretrieving hook portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The various embodiments will be described in detail with reference tothe accompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicates a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. Also, as used herein, the terms “patient”,“host” and “subject” refer to any human or animal subject and are notintended to limit the systems or methods to human use, although use ofthe subject invention in a human patient represents a preferredembodiment.

FIGS. 1-14 illustrate the preferred embodiments. Referring to FIG. 1, afilter 100 is illustrated in a perspective view. The filter 100 includesa hub 10, locator member 20, and anchor member 30 that has a hook 40.The filter 100 can be made from a plurality of elongate wires, which arepreferably metal, such as, for example, Elgiloy, and more preferably area super elastic shape memory alloy, such as Nitinol. The wires are heldtogether at the filter trailing end by a hub 10 by a suitable connectiontechnique, such as, for example, welding, laser welding, or plasmawelding or being bonded together. Preferably, the wires are plasmawelded. As used herein, “wire” refers to any elongated member of narrowcross section, including rods, bars, tubes, wire and narrow sections cutfrom thin plate, and is not intended to limit the scope of the inventionto elongated members of circular cross section, cut from wire stock ormanufacture according to a particular method of metal forming.

The locator member 20 has a proximal locator end 20P and a distallocator end 20D. Similarly, the anchor member 30 has a proximal anchorend 30P and a distal anchor end 30D. The distal anchor end 30D can beprovided, as shown in FIG. 6, with hook 40.

Referring to FIGS. 4A and 4B, the locator member 30 may be provided witha plurality of locator segments, preferably between 3 and 6 segments andmore preferably four locator segments LS1, LS2, LS3, LS4. First locatorsegment LS1 may be a curved portion extending away from the hub in afirst direction along the longitudinal axis A. In an embodiment, thesecond locator segment LS2 extends generally linearly along a secondaxis 110; third locator segment LS3 extends generally linearly along athird axis 120; and the fourth locator segment LS4 extends generallylinearly along a fourth axis 130. In a preferred embodiment, the variousaxes A, 110, 120, 130, and 140 are distinct from one another in thateach may intersect with one another but none of them are substantiallycollinear with each other.

The locator segment LS2 may be distinct from locator segment LS3 byvirtue of a joint or bend LJ1. The locator segment LS3 may be distinctfrom locator segment LS4 via a join or bend LJ2. The joint or bend LJ1or LJ2 can be viewed as a location formed by the intersection of thesegments defining a radiused portion connecting any two segments.

The locators 20 may range from 3 to 12 locators. The filter embodimentillustrated in FIG. 4A includes six locators that are generallyequiangularly spaced about axis A. In the embodiment illustrated in FIG.4B, locator segment LS1 extends through an arc with a radius ofcurvature R1 whose center may be located along an axis orthogonal toaxis A over a radially transverse distance d₃ and over a longitudinaldistance L₄ as measured from a terminal surface 12 of the hub 10 alongan axis generally parallel to the longitudinal axis A. The locatorsegment LS2 extends along axis 110 to form a first angle θ₁ with respectto the longitudinal axis A whereas the locator segment LS3 extends alongaxis 120 to form second angle θ₂. As shown in FIG. 4B, the first locatorjoint or bend LJ1 may be located at a longitudinal length L₁ generallyparallel to axis A from the terminal surface 12. The first locator jointor bend LJ1 may be also located at a distance of about one-half distance“d₁” from axis A on a generally orthogonal axis with respect to axis Aas shown in FIG. 4A, where the distance d₁ is the distance betweeninside facing surfaces of respective diametrically disposed locators 20.The second locator joint LJ2 may be located over a longitudinal lengthL₂ generally parallel to axis A. The second locator join LJ2 may belocated over a distance of about one-half diameter “d₂” from axis A. Thedistance d₂ is the distance between the outermost surface of the fourthsegment LS4 of respective diametrically disposed locators 20. Thethickness of locator member 20 is t₁. Where the locator member 20 is awire of circular cross-section, the thickness t₁ of the locator 20 maybe the diameter of the wire.

A range of values may be used for the aforementioned dimensionalparameters in order to provide locator members that will locate thefilter within the vein or vessel in which the filter is to be applied ina manner that positions segment LS4 approximately parallel to the wallsof the vein or vessel and provides sufficient lateral force against thevein or vessel wall to center the filter but not so much force as tocause injury to the wall. For example, a filter intended to be placed ina narrow vein or vessel, such as a human infant or canine vena cava, mayhave smaller dimensions L₁, L₂, L₃, L₄, LS1, LS2, LS3, LS4, d₁ and d₂ sothat the positioning members can deploy sufficiently to accomplish thepositioning and filtering functions, than a filter intended to be placedin a large vein or vessel, such as an adult human vena cava or othervessel. In an example embodiment suitable for an adult human vena cavafilter, when the filter is at the temperature of the subject andunconstrained, the radius of curvature R₁ is from about 0.02 inches toabout 0.1 inches with the center of the radius R₁ being located over adistance d₃ from the axis A of about 0.1 inches and length L₄ of about0.2 inches; the length L₁ is about 0.3 inches; length L₂ is about 0.9inches; distance d₁ (as measured to the inside facing surfaces ofdiametrically disposed locators 20) is about 0.8 inches; distance d₂ isabout 1.5 inches, the first angle θ₁ is about 58 degrees, the secondangle θ₂ is about 22 degrees; and the thickness t₁ of the locator isabout 0.013 inches. It should be noted that the values given herein areapproximate, representing a dimension within a range of suitabledimensions for the particular embodiment illustrated in the figures, andthat any suitable values can be used as long as the values allow thefilter to function as intended in a blood vessel of a subject.

Referring to FIGS. 5A and 5B, the hub 10 can be provided with aninternal cylindrical opening with a diameter of about two times thedistance d₈. Each of the plurality of anchor members 30 can be providedwith a first anchor segment LA1, a portion of which is disposed withinthe hub 10, connected to a second anchor segment LA2 by a first anchorjoint or bend AJ1, which can be connected to a third anchor segment LA3via a second anchor joint or bend AJ2. The third anchor segment LA3 canbe connected to the hook 40 via third anchor joint or bend AJ3. Thefirst anchor segment LA1 extends obliquely with respect to axis A. Thesecond anchor segment LA2 extends along axis 130 oblique with respect tothe axis A over an angle θ₃ with respect to the longitudinal axis A. Thethird anchor segment LA3 extends along axis 140 oblique with respect tothe longitudinal axis A over an angle θ₄. The second anchor joint orbend AJ2 can be located at a sixth longitudinal distance L₆ as measuredon an axis generally parallel to the axis A from the terminal surface 12of the hub 10 and at about one half the fourth distance d₄ as measuredbetween generally diametrical end points of two anchors 30 on an axisgenerally orthogonal to the axis A. The third anchor joint AJ3 can belocated at a seventh longitudinal distance L₇ as measured along an axisgenerally parallel to axis A and at a transverse distance of aboutone-half distance d₇ as measured on an axis orthogonal to the axis Abetween the inner surfaces of two generally diametric anchors 30. Thethickness of anchor member 30 is nominally t₂. Where the anchor member30 is a wire of circular cross-section, the thickness t₂ of the anchor30 may be the diameter of the wire. As shown in FIG. 5B, the hook 40 maybe contiguous to a plane located at a longitudinal distance of L₁₀ asmeasured to the terminal surface 12 of hub 10. The hook 40 can becharacterized by a radius of curvature R₂, in its expanded configurationat a suitable temperature, e.g., room temperature or the internaltemperature of a subject. The center of the hook curvature R₂ can belocated at a distance L₁₁ as measured along an axis generally parallelto the axis A from the terminal surface 12 of hub 10 and at one-halfdistance d₆ as measured between two generally diametrical hooks 40. Thetips 40T of respective diametric hooks 40 may be located at longitudinaldistance L₁₂ (which may be approximately the same as longitudinaldistance L₇ to the third anchor joint AJ3) and at one half of distanced₇ between diametric hooks 40.

A range of values may be used for the aforementioned dimensionalparameters in order to provide anchor members that will locate andanchor the filter within the vein or vessel in which the filter is to beapplied in a manner that positions hooks 40 in contact with the walls ofthe vein or vessel and provides sufficient lateral force against thevein or vessel wall to ensure the hooks engage the wall but not so muchforce as to cause injury to the wall. For example, a filter intended tobe placed in a narrow vein or vessel, such as a child or dog vena cava,may have smaller dimensions so that the anchor members can deploysufficiently to accomplish the positioning, anchoring and filteringfunctions, than a filter intended to be placed in a large vein orvessels, such as an adult vena cava or other vessel. In an exampleembodiment suitable for an adult human vena cava filter, when the filteris at the temperature of the subject and unconstrained, the longitudinaldistance L₈ is about 0.02 inches; L₉ is about 0.2 inches; L₁₀ is about1.3 inches; L₁₁ is about 1.2 inches; d₆ is about 1.5 inches; d₇ is about1.6 inches; d₈ is about 0.01 inches; d₉ is between 1.5 and 1.6 inches;L₁₂ is about 1.2 inches; the radius of curvature R₂ is about 0.03inches; and the thickness t₂ of the anchor member is about 0.013 inches.Most preferably, a very small radius of curvature R₃ can characterizeanchor joint or bend AJ2 where R₃ can be about 0.01 inches.

In situations where additional retention of the filter may be desired,an anchor member can be coupled to the locator. One arrangement is shownexemplarily in FIG. 5C, where a hook 22 can be coupled to the locatorproximate the tip portion. In this arrangement, both the tip portion andhook 22 are configured so that the locator does not penetrate throughthe blood vessel wall by formation of a stop region 22 a defined by boththe locator tip and the hook 22. Another arrangement can be by couplingor forming a hook in the same configuration as hook 40 for the anchormembers. In yet another arrangement, shown here in FIG. 5D, where it maynot be desirable to utilize a hook, one or more stop members 24 can beprovided on the locator at any suitable locations. As shown in FIG. 5D,the stop member 24 is in the form of a truncated cone coupled to thelocator. However, the stop member 24 can be of any configuration as longas the member 24 reduces or prevents penetration of the locator throughthe blood vessel wall. And in yet a further arrangement, the hook 22 (orhook 40) can be utilized in combination with the stop member 24 such asfor example, a hook 22 coupled to a first locator, a hook 40 coupled toa second locator, a stop member 24 on a third locator, a combination ofhook 22 and stop member 24 on a fourth locator, a combination of hook 40and stop member 24 on a fifth locator.

Referring to FIG. 6, the hook 40 can be provided with a proximal hookportion 40P and a distal hook portion 40D on which a sharpened tip 40Tis provided. The hook 40 can be formed to have a thickness t₃. Where thehook 40 is formed from a wire having a generally circular cross-section,the thickness t₃ may be generally equal to the outside diameter of thewire. In an embodiment, the hook thickness t₃ is approximately 0.5 toapproximately 0.8 that of the anchor thickness t₂. The wire can beconfigured to follow a radius of curvature R₂ whose center is located atlongitudinal distance L₁₁ and radial distance d₉ when the filter is atthe temperature of a subject, as discussed above. The tip 40T can beprovided with a generally planar surface 40D whose length can beapproximately equal to length h₁. The tip 40T may be located over adistance h₂ from a plane tangential to the curved portion 40S.

Referring to FIG. 7, the locators 20 are illustrated has being boundedby a first compound surface of revolution SR1 about axis A by rotatingone of the locators 20 about axis A for 360 degrees. The first compoundsurface of revolution SR1 includes a portion of a truncated hyperboloidH, first frustum F1, second frustum F2, and cylindrical surface C1. Withreference to FIG. 8, the anchors 30 are illustrated as being bounded bya second compound surface of revolution SR2 about axis A by rotating oneof the anchors 30 about axis A for 360 degrees. The second compoundsurface of revolution SR2 defined by the anchors 30 includes a third,fourth and fifth frustums F3, F4, and F5, respectively.

Several design parameters are believed to allow the preferredembodiments to achieve various advantages over the known filters. Thevarious advantages include, for example, resisting migration of thefilter 100 once installed, greater filter volume, and betterconcentricity with respect to the inner wall of the blood vessel. Anumber of design parameters may be adjusted to effect performance andfit characteristics of the filter, including, for example, the ratio ofthe volume V₁ defined by the first surface of revolution SR1 to thevolume V₂ defined by the second surface of revolution SR2, which may beat least 0.92, preferably about 1.0, and most preferably about 0.99.Also, approximately 15% or more of the volume V₂ may be surrounded bythe volume V₁, preferably at least 25% of the volume V₂ may besurrounded by the volume V₁, and most preferably, about 35% of thevolume V₂ may be surrounded by volume V₁ so that the portion of volumeV₂ that is not surrounded by volume V₁ (i.e., the volume of V₁ outsidethe first volume V₁), shown as volume V₃ in FIG. 9, is about 0.4 cubicinches. Also, it has been discovered that, in the preferred embodiments,as the cross-sectional area of the hook is increased, the filter 100tends to resist dislodgement when installed in a simulated blood vessel.Similarly, when the radius of curvature R₂ is decreased, while keepingother parameters generally constant, the resistance to dislodgement in asimulated blood vessel is increased.

The material for the filter may be any suitable bio-compatible materialsuch as, for example, polymer, memory polymer, memory metal, thermalmemory material, metal, metal alloy, or ceramics. Preferably, thematerial may be Elgiloy, and most preferably Nitinol which is a thermalshape memory alloy.

The use of a shape memory material, such as Nitinol, for the locator andanchor members facilitates collapsing the filter radially inward fromits normally expanded (i.e., unconstrained) configuration toward itslongitudinal axis into a collapsed configuration for insertion into abody vessel. The properties of Nitinol allow the filter members towithstand enormous deformations (e.g. 8 times as much as stainlesssteel) without having any effect of the filter ability to recover to thepre-determined shape. This is due to the crystal phase transitionsbetween rigid austenite and softer martensite. This phenomenon enablesthe implant to be loaded into a very small diameter sheath for delivery,which significantly reduces the trauma and complications to theinsertion site.

Transition between the martensitic and austenitic forms of the materialcan be achieved by increasing or decreasing the material deformationabove and below the transition stress level while the material remainsabove the transition temperature range, specifically A_(f). This isparticularly important in the case of the hooks, as they may be deformedsignificantly (hence, becoming martensitic) while the filter ischallenged by clots. The super-elastic properties will allow the hooksto re-assume their intended shape as soon as the load is released (e.g.the clot breaks down).

The hooks may be retrieved from the Inferior Vena Cava (“IVC”) wallduring the filter removal when longitudinal force is applied to the hub10 in the direction of the BF (i.e., towards the hub 10 of the filter).Under this concentrated stress, the hooks will straighten and transitionto the martensitic state, thereby becoming super-elastic. Thus the hooks40 are designed to bend toward a substantially straight configurationwhen a specific hook migration force is applied and spring back to theiroriginal shape once the hook migration force is removed.

Alternatively, a reduction in temperature below the A_(f) temperaturecan be applied to the shape memory material to cause a change in thecrystalline phase of the material so as to render the material malleableduring loading or retrieval of the filter. Various techniques can beused to cause a change in crystalline phase such as, for example, coldsaline, low temperature fluid or thermal conductor.

By virtue of the characteristics of thermal shape memory material, thelocator and anchor members can be cooled below themartensitic-to-austenitic transition temperature, and then straightenedand held in a collapsed, straight form that can pass through a length offine plastic tubing with an internal diameter of approximately 2millimeters (mm), e.g., a #8 French catheter. In its high temperatureform (as in a mammalian body), the filter 10 recovers to a preformedfiltering shape as illustrated by FIG. 1. Alternatively, the locatorand/or anchor members may be made of wires of spring metal which can bestraightened and compressed within a catheter or tube and will divergeinto the filter shape of FIG. 1 when the tube is removed.

The deployed shapes and configurations of the filter members can be set(imprinted with a memory shape) by annealing the members at hightemperature (e.g. approximately 500° C.) while holding them in thedesired shape. Thereafter, whenever the filter is in the austenitic form(i.e., at a temperature above the martensitic-to-austenitic transitiontemperature or A_(f) temperature), the members return to the memoryshape. Example methods for setting the high-temperature shape of filtersare disclosed in U.S. Pat. No. 4,425,908, the contents of which arehereby incorporated by reference in their entirety.

In the high-temperature form of the shape memory material, the filterhas generally coaxial first and second filter baskets or sieves, eachfilter basket being generally symmetrical about the longitudinal axis ofthe filter with both filter baskets being concave relative to the filterleading end.

The sieve V₂ formed by anchor members 30 is the primary filter and canbe up to twelve circumferentially spaced anchor members 30. Six anchormembers 30 are shown in the embodiment illustrated in the figures. Theanchor members may be of equal length, but may be of different length sothat the hooks 40 at the ends of the wires will fit within a catheterwithout becoming interconnected. The anchor members 30, in theirexpanded configuration illustrated in FIG. 1 (i.e., unconstrained in thehigh temperature form), are at a slight angle to the vessel wall,preferably within a range of from ten to forty-five degrees, while thehooks 40 penetrate the vessel wall to anchor the filter againstmovement. The anchor members 30 are radially offset relative to thelocator members 20 and may be positioned radially halfway between thelocator members 20 and also may be circumferentially spaced by sixtydegrees of arc as shown in FIG. 3. The locator members 20 form sieve V₁.Thus, the combined filter sieves V₂ and V₁ can provide a wire positionedradially about the hub 10, such as at every thirty degrees of arc at themaximum divergence of the filter sections. With reference to thedirection of blood flow BF shown by the arrow in FIGS. 2 and 4A, in theillustrated embodiment, the filter section V₂ forms a frustum toward thehub 10 of the filter 100 while the filter section V₁ forms a generallyfrustum-like concave sieve with its geometric center proximate theterminal end 12 of the hub 10. In the preferred embodiments, the volumeV₁ of the surface SR1 may be between about 0.3 and about 1.1 cubicinches, preferably about 0.7 cubic inches and the volume V₂ of thesurface SR2 may be between about 0.3 and about 1.1 cubic inches,preferably about 0.7 cubic inches.

The structure of the hooks 40 is believed to be important in resistingmigration of the filter once installed while allowing for removal fromthe blood vessel after installation. As in the case of hooks formed onthe anchor members of known permanent vena cava filters, these hooks 40penetrate the vessel wall when the filter 100 is expanded to anchor thefilter in place and prevent filter migration longitudinally within thevessel in either direction. However, when the hooks 40 are implanted andsubsequently covered by the endothelium layer, they and the filter canbe withdrawn without risk of significant injury or rupture to the venacava. Minor injury to the vessel wall due to hook withdrawal such asdamage to the endothelial layer or local vena cava wall puncture isacceptable.

To permit safe removal of the filter, the juncture section 40S may beconsiderably reduced in cross section relative to the thickness t₂ orcross section of the anchor member 30 and the remainder of the hook 40.The juncture section 40S can be sized such that it is of sufficientstiffness when the anchor members 30 are expanded to permit the hook 40to penetrate the vena cava wall. However, when the hook is to bewithdrawn from the vessel wall, withdrawal force in the direction ofblood flow BF will cause flexure in the juncture section 40S so that thehook tip 40T moves toward a position parallel with the axis A (i.e., thehook straightens). With the hooks so straightened, the filter can bewithdrawn without tearing the vessel wall while leaving only smallpunctures. In an embodiment, the anchor member 30 has a cross-sectionalarea of about 0.00013 squared inches, and the hook 40, particularly thecurved junction section 40S has a cross-sectional area of about 0.000086squared inches.

With reference to FIG. 6, it will be noted that the entire hook 40 canbe formed with a cross section t₃ throughout its length that is lessthan that of the locator 20 members (which have thickness t₁) or anchormembers 30 (which have thickness t₂). As a result, an axial withdrawalforce will tend to straighten the hook 40 over its entire length. Thiselasticity in the hook structure is believed to prevent the hook fromtearing the vessel wall during withdrawal.

As previously indicated, while it is possible that the filter could bemade from ductile metal alloys such as stainless steel, titanium, orElgiloy, it is preferable to make it from Nitinol. Nitinol is a lowmodulus material that allows the locator and anchor members of thedevice 100 to be designed to have low contact forces and pressures whilestill achieving sufficient anchoring strength to resist migration of thedevice. The force required to cause opening of the hooks 40 can bemodulated to the total force required to resist filter migration. Thisis accomplished by changing the cross sectional area or geometry of thehooks, or by material selection, as discussed above.

In addition to temperature sensitivity, when in the high temperatureaustenitic state, Nitinol is also subject to stress sensitivity that cancause the material to undergo a phase transformation from the austeniticto the martensitic state while the temperature of the material remainsabove the transition temperature. By reducing the cross sectional areaof a portion or all of the hooks 40 relative to that of the anchormembers 30 or locator members 20, stress will be concentrated in theareas of reduced cross section when longitudinal force is applied to thehub 10 in the direction of the BF (i.e., towards the hub 10 of thefilter) such as to remove the filter. Under this concentrated stress,the reduced cross section portions of the hooks may transition to themartensitic state, thereby becoming elastic so that they straighten.Thus the hooks 40, whether formed of Nitinol, Elgiloy, spring metal orplastic, are designed to bend toward a substantially straightconfiguration when a specific hook migration force is applied and springback to their original shape once the hook migration force is removed.

The force or stress that is required to deform the hooks 40 can becorrelated to the force applied to each hook of the device when it isfully occluded and the blood pressure in the vessel is allowed to reach50 millimeters of mercury (mm Hg) in a test stand. The test stand (notshown) can be configured to have a length of tubing (with variousinternal diameters) to allow a filter to be suitably attached thereto.The tubing is connected to another tubing having a terminal end exposedto ambient atmosphere and marked with gradations to indicate the amountof pressure differential across the filter, which is related to theforce being applied to each anchor of the filter 100. This force isapproximately at least 70 grams on each anchor of a six-anchor devicefor at least 50 millimeters Hg pressure differential in a 28 mm vessel.The desired total migration resistance force for the filter is believedto be approximately 420 grams for the embodiment of a vena cava filterfor an adult human subject, and more anchor members 30 with hooks 40 canbe added to lower maximum migration force for each hook. The load on thefilter would be correspondingly smaller in vessels of smaller diameter.Preferably the hooks 40 perform as an anchoring mechanism at apredetermined filter migration resistance force within a range of about10 mm Hg up to about 150-200 mm Hg. Having maintained its geometry at apredetermined filter migration resistance force within this range, thehook 40 preferably begins to deform in response to a higher forceapplied in the direction of the hub, i.e., the filter trailing end TEwith respect to blood flow, and release at a force substantially lessthan that which would cause damage to the vessel tissue. It is theability of the hook to straighten somewhat that allows for safe removalof the preferred embodiment filters from the vessel wall.

After the filter 100 has remained in place within a blood vessel for aperiod of time in excess of two weeks, the endothelium layer will growover the hooks 40. However, since these hooks 40, when subjected to awithdrawal force in the direction of the hub (i.e., toward the trailingend TE) become substantially straight sections of wire oriented at asmall angle to the vessel wall, the filter can be removed leaving onlysix pin point lesions in the surface of the endothelium. To accomplishthis, a catheter such as, for example, the unit described and shown inU.S. Pat. No. 6,156,055, which is incorporated by reference herein, orsimilar retrieval unit is inserted over the hub 10 and into engagementwith the locator members 20. While the hub 10 is held stationary, thecatheter may be moved downwardly, forcing the locator members 20 to foldtowards the axis A, and subsequently engaging the anchor members 30 andforcing them downwardly thereby withdrawing the hooks 40 from theendothelium layer. Then the hub 10 may be drawn into the catheter tocollapse the entire filter 100 within the catheter. When the filter isformed from shape memory material, cooling fluid (e.g., chilled saline)may be passed through the catheter during these steps to aid incollapsing the filter.

The primary objective of the hooks 40 is to ensure that the filter doesnot migrate during normal respiratory function or in the event of amassive pulmonary embolism. Normal inferior vena cava (IVC) pressuresare believed to be between about 2 mm Hg and about 8 mm Hg. An occludedIVC can potentially pressurize to 35 mmHg below the occlusion. To ensurefilter stability, a 50 mm Hg pressure drop across the filter maytherefore be chosen as the design criteria for the filter migrationresistance force for the removable filter 100. When a removal pressureis applied to the filter that is greater than at least 50 millimetersHg, the hooks 40 will deform and release from the vessel wall. Thepressure required to deform the hooks can be converted to force by thefollowing calculations.

Since 51.76 mm Hg=1.0 pounds per square inch (psi), 50 mm Hg=0.9668 psi

For a 28 mm vena cava:

$\begin{matrix}{A = {\frac{\pi}{4}(28)^{2}\mspace{14mu}{mm}^{2}}} \\{= {615.4\mspace{14mu}{mm}^{2}}} \\{= {0.9539\mspace{14mu}{inches}^{2}}}\end{matrix}$

Migration force is calculated by:

$P = \frac{F}{A}$ F = P × A0.9668  psi × 0.9539  inches² = 0.9223  pounds = 418.7  grams

It should be noted that as the vena cava diameter increases so does theforce required to resist at least 50 millimeters Hg of pressure.

Depending on the number of filter hooks, the strength of each can becalculated. For a device that has six hooks:

$\begin{matrix}{{{Hook}\mspace{14mu}{Strength}} = \frac{{Filter}\mspace{14mu}{Migration}\mspace{14mu}{Resistance}\mspace{14mu}{Force}}{{Number}\mspace{14mu}{of}\mspace{14mu}{Hooks}}} \\{= \frac{418.7}{6}} \\{= {69.7\mspace{14mu}{grams}}}\end{matrix}$

In other words, each hook must be capable of resisting approximately atleast 70 grams of force for the filter 100 to resist at least 50millimeters Hg pressure gradient in a 28 mm vessel.

To prevent excessive vessel trauma each individual hook needs to berelatively weak. By balancing the number hooks and the individual hookstrength, minimal vessel injury can be achieved while still maintainingthe at least 50 millimeters Hg pressure gradient criteria, or some otherpredetermined pressure gradient criteria within a range of from 10 mmHgto 150 mm Hg.

Referring to FIG. 4A, the anchor members 30 may be angled outwardly fromthe anchor joint or bend AJ1 adjacent to but spaced from the outer endof each anchor member 30. When the anchor members 30 are released fromcompression in a catheter or other tube into a body vessel, this bend ineach anchor member insures that the hooks 40 are, in effect, springloaded in the tube and that they will not cross as they are deployedfrom the tube. Since the anchor members 30 angled outwardly from theshoulders 30, the hooks 40 are rapidly deployed outwardly as theinsertion tube is withdrawn.

In another embodiment, bio-active agents can be incorporated with theblood filter, such as by way of a coating on parts of the filter, ordissolvable structures on, within or attached to the filter. Bio-activeagent may be included as part of the filter in order to treat or preventother conditions (such as infection or inflammation) associated with thefilter, or to treat other conditions unrelated to the filter itself.More specifically, bio-active agents may include, but are not limitedto: pharmaceutical agents, such as, for example,anti-proliferative/antimitotic agents including natural products such asvinca alkaloids (i.e. vinblastine, vincristine, and vinorelbine),paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide),antibiotics (dactinomycin (actinomycin D) daunorubicin, doxorubicin andidarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin(mithramycin) and mitomycin, enzymes (L-asparaginase which systemicallymetabolizes L-asparagine and deprives cells which do not have thecapacity to synthesize their own asparagine); antiplatelet agents suchas G(GP) IIb/IIIa inhibitors and vitronectin receptor antagonists;anti-proliferative/antimitotic alkylating agents such as nitrogenmustards (mechlorethamine, cyclophosphamide and analogs, melphalan,chlorambucil), ethylenimines and methylmelamines (hexamethylmelamine andthiotepa), alkyl sulfonates-busulfan, nirtosoureas (carmustine (BCNU)and analogs, streptozocin), and trazenes-dacarbazinine (DTIC);anti-proliferative/antimitotic antimetabolites such as folic acidanalogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine,and cytarabine), purine analogs and related inhibitors (mercaptopurine,thioguanine, pentostatin and 2-chlorodeoxyadenosine {cladribine});platinum coordination complexes (cisplatin, carboplatin), procarbazine,hydroxyurea, mitotane, aminoglutethimide; hormones (i.e. estrogen);anti-coagulants (heparin, synthetic heparin salts and other inhibitorsof thrombin); fibrinolytic agents (such as tissue plasminogen activator,streptokinase and urokinase), aspirin, dipyridamole, ticlopidine,clopidogrel, abciximab; antimigratory agents; antisecretory agents(e.g., breveldin); anti-inflammatory agents, such as adrenocorticalsteroids (cortisol, cortisone, fludrocortisone, prednisone,prednisolone, 6.alpha.-methylprednisolone, triamcinolone, betamethasone,and dexamethasone), non-steroidal agents (salicylic acid derivativesi.e. aspirin; para-aminophenol derivatives i.e. acetominophen; indoleand indene acetic acids (indomethacin, sulindac, and etodalac),heteroaryl acetic acids (tolmetin, diclofenac, and ketorolac),arylpropionic acids (ibuprofen and derivatives), anthranilic acids(mefenamic acid, and meclofenamic acid), enolic acids (piroxicam,tenoxicam, phenylbutazone, and oxyphenthatrazone), nabumetone, goldcompounds (auranofin, aurothioglucose, gold sodium thiomalate);immunosuppressives: (cyclosporine, tacrolimus (FK-506), sirolimus(rapamycin), azathioprine, mycophenolate mofetil); angiogenic agents,such as vascular endothelial growth factor (VEGF), fibroblast growthfactor (FGF); angiotensin receptor blockers; nitric oxide donors;anti-sense oligionucleotides and combinations thereof; cell cycleinhibitors, such as mTOR inhibitors, and growth factor receptor signaltransduction kinase inhibitors; retenoids; cyclin/CDK inhibitors; HMGco-enzyme reductase inhibitors (statins); and protease inhibitors.

A filter delivery unit (not shown) such as, for example, the unitdescribed in U.S. Pat. No. 6,258,026, which is incorporated by referenceherein, is adapted to deliver the filter 100 through a catheter ordelivery tube to a generally centered position within a blood vessel, asdescribed in further detail in the above mentioned patent. Preferably,the delivery system may be the delivery system shown and described inU.S. Provisional Patent Application No. 60/706,596, entitled “EmbolusBlood Clot Filter and Delivery System,” filed on Aug. 9, 2005, or thedelivery system shown and described in a patent application that claimspriority to the antecedent provisional patent application, PCT PatentApplication No. PCT/US2006/017890 entitled “Embolus Blood Clot Filterand Delivery System” filed on May 9, 2006; and both applications arehereby incorporated by reference in their entirety into thisapplication.

In an embodiment, a radio-opaque material can be incorporated in aportion of the filter, preferably the hub 10 of the filter. As usedherein, a radio-opaque material is any material that is identifiable tomachine or human readable radiographic equipment while the material isinside a mammal body, such as, by way of example but not by way oflimitation, gold, tungsten, platinum, barium sulfate, or tantalum. Theuse of a radio-opaque material in the filter permits the clinician tolocate the filter within a blood vessel of the subject usingradiographic equipment. Radio-opaque material may be in the form of anadditional structure added to the hub, such as a cap, sleeve, shim, wireor braze included around or in the hub assembly. Alternatively, the hubitself may be formed of a radio-opaque alloy.

Instead of a hub 10, as in the above described embodiments, a retrievinghook can be provided as part of filter device 200, as in the embodimentshown in FIG. 10. The filter device 200 includes a hub 210 with aretrieving hook 220. The hook 220 is configured for use by a snaringdevice to retrieve the filter 200 from a subject. Referring to FIGS. 11and 12, the retrieving hook 220 can be formed as a monolithic member 230with the hub 210 or as a separate member joined to the hub 210 by asuitable technique, such as, for example, EDM, laser welding, plasmawelding, welding brazing, welding, soldering, or bonding. In a preferredembodiment, the member 230 can be a machined billet member with a blindbore 240 formed through a portion of the hub 210. The hook portion 220includes ramped surfaces 250 and 260 that are believed to beadvantageous in allowing the filter 200 to be retrieved without bindingat the catheter opening due to an offset entry position of the filter200. In other words, there may be circumstances during removalprocedures where the axis 300 of the member 230 is not generallyparallel or aligned with a longitudinal axis of the catheter retrievingdevice. In such cases, the greater the retention force, it is believedthat the greater the likelihood of the hook being snagged on thecatheter inlet opening thereby complicating the filter retrievalprocess. By virtue of the ramps 250 and 260, it is believed that bindingor snagging is substantially reduced. In particular, as shown in FIGS.13 and 14, the ramp 250 includes a radius of curvature R4 coupled toflat portions 252 and 254. The flat portion 254 can be coupled to a hookportion 256 which has a radiused surface R6. As shown in FIG. 13, theflat portion 252 is coupled to another radiused portion R7. It should benoted that the drawings provided herein are to scale relative to everypart illustrated in each drawing.

A range of values may be used for the aforementioned dimensionalparameters in order to provide a retrieval hook 230 that is capable ofretaining portions of the locator and anchor members 20 and 30 withinblind hole 240. For example, a smaller filter may have smallerdimensions so that the retrieval hook 230 does not present undueblockage in the vein, than a filter intended to be placed in a largevein or vessels, such as an adult vena cava or other vessel. Further,the retrieval hook 230 may be made from or include a radio-opaquematerial to allow a clinician to locate the hook within a subject usingradiographic equipment, such as to aid in engaging the hook with aretrieval mechanism.

While the present invention has been disclosed with reference to certainpreferred embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the present invention, as defined in the appendedclaims. Accordingly, it is intended that the present invention not belimited to the described embodiments, but that it have the full scopedefined by the language of the following claims, and equivalentsthereof.

What is claimed is:
 1. A filter to be placed in a flow of blood througha vessel, the filter comprising: a hub disposed along a longitudinalaxis; at least one anchor member projecting from the hub, the at leastone anchor member including a hook that penetrates a blood vessel wallwhen the filter is placed in a blood vessel, the hook spaced along thelongitudinal axis from the hub and spaced a first radial distance fromthe longitudinal axis; and at least one locator member projecting fromthe hub, the at least one locator member including a tip segment spacedalong the longitudinal axis from the hub and spaced a second radialdistance from the longitudinal axis, wherein the second radial distanceis less than the first radial distance, the at least one locator memberhaving at least four segments including the tip segment, each disposedon respective distinct axes, the four segments comprising: a proximalsegment proximate the hub; a first linear segment that extends from theproximal segment along a first angle with respect to the longitudinalaxis; a second linear segment that extends from the first segment alonga second angle with respect to the longitudinal axis, wherein the secondangle is less than the first angle; and the tip segment that extendsfrom the second segment along a third angle with respect to thelongitudinal axis, wherein the third angle is less than the secondangle.
 2. The filter according to claim 1, wherein the proximal segmentincludes a curved portion that extends along the longitudinal axis on aradius of curvature.
 3. The filter according to claim 2, wherein thecurved portion comprises a radius of curvature of about 0.1 inches aboutan axis generally orthogonal to the longitudinal axis.
 4. The filteraccording to claim 1, wherein the hook is offset in alignment withrespect to the axis on which at least one segment of the anchor memberis aligned.
 5. The filter according to claim 1, wherein the at least oneanchor member comprises: a first anchor segment that extends away fromthe longitudinal axis at a fourth angle; a second anchor segment thatextends away from the longitudinal axis at a fifth angle; and aretention portion.
 6. The filter according to claim 5, wherein the atleast one locator member comprises two locator members that define afirst virtual circle having a first diameter extending through thelongitudinal axis.
 7. The filter according to claim 6, wherein the twolocator members include a hook to engage with the wall of the bloodvessel.
 8. The filter according to claim 6, wherein the at least oneanchor member comprises two anchor members that define a second virtualcircle having a second diameter extending through the longitudinal axis,the second diameter being about 1.2 times the first diameter.
 9. Thefilter according to claim 5, wherein the retention portion comprises ahook.
 10. The filter according to claim 9, wherein the hook comprises acurved configuration in an operative condition and a generally linearconfiguration in a constrained condition.
 11. The filter according toclaim 10, wherein the hook comprises a curved configuration in anoperative condition and an anchor member is twisted about its axis in aconstrained condition of the filter.
 12. The filter according to claim10, wherein the hook is in the constrained condition when at least aboutat least 70 grams of force or more is applied to each locator along thelongitudinal axis.
 13. The filter according to claim 12, wherein thefirst and second anchor segments comprise a cross-sectional area ofabout 0.00013 squared inches.
 14. The filter according to claim 13,wherein the hook comprises a curved member having a cross-sectional areaof about 0.000086 squared inches.
 15. The filter according to claim 1,wherein the tip segment comprises a length along the longitudinal axisof about 0.05 inches.
 16. The filter according to claim 1, wherein theat least one anchor member comprises a plurality of anchor members witha plurality of hooks, wherein the at least one locator member comprisesa plurality of locator members with a plurality of tip segments, andwherein the hooks define a first circle having a radius equal to thefirst distance, and the tip segments define a second circle having aradius equal to the second distance, the first and second circles beinggenerally concentric about the longitudinal axis.
 17. The filteraccording to claim 1, further comprising a bio-active agent.
 18. Thefilter according to claim 1, further comprising a bio-active agentcoupled to the filter and a radiopaque material disposed proximate thehub.